A motor vehicle having an idling-stop system is under a development, wherein an engine operation is stopped to reduce carbon dioxides in exhaust gas from an internal combustion engine and to improve a fuel consumption ratio, in the case that the engine operation is in an idling operation and a time period for the idling operation exceeds a predetermined amount. When a clutch for an automatic transmission device is decoupled so that the automatic transmission device is disconnected from the engine during the engine operation is stopped under the idling-stop system, a delay for mechanical coupling at the clutch occurs at a re-start of the engine operation to move the vehicle. When such a delay occurs, a shock is generated at starting the vehicle, thereby decreasing a comfortable ride. To this end, the idling-stop system has been proposed in the prior arts, in which an electric oil pump is additionally provided in parallel with a mechanical oil pump, which is driven by an engine and supplying pressurized working fluid to the clutch for the automatic transmission device, so that the working fluid is continuously supplied from the electric oil pump to the clutch during the idling-stop of the engine. For example, such system is disclosed in Japanese Patent Publication No.2000-046166 and No.2001-280458.
In the above prior arts, however, an output side of the electric oil pump is connected not only to the clutch but to other oil circuits having mechanical devices other than the automatic transmission device. For example, the oil circuits include a lubricating device, a device for torque converter, and so on, which generally consume a larger quantity of working fluid. In those prior art system, the working fluid discharged from the electric oil pump flow into not only the clutch but those other oil circuits. As a result, a larger size of the electric oil pump is necessary because a larger quantity of the discharged working fluid is necessary to keep the mechanical coupling at the clutch.
In another prior art, for example as disclosed in Japanese Patent Publication No.2002-195399, the working fluid discharged from the electric oil pump is directly supplied to the clutch in order to avoid a large-sized electric oil pump. According to this prior art, the working fluid is prevented from flowing into the other oil circuits than the clutch.
It is, however, disadvantageous in this prior art in the following situation. The motor vehicle with the automatic transmission device has a shift lever, and the motor vehicle and/or the engine is controlled by and in accordance with a position of the shift lever. For example, when the shift lever is positioned at “P-range” or “N-range”, the clutch between the engine and the automatic transmission device is generally decoupled.
When any problem occurs in the oil circuit between the electric oil pump and the clutch and/or when the operation of the electric oil pump can not be stopped, the working fluid may be continuously supplied from the electric oil pump to the clutch even in the case that the shift lever is moved to “N-range” or “P-range”.